1. Field of the Invention
The present invention relates to an apparatus for an improved camera lens and filter adapter assembly, and more particularly, to a camera lens assembly which can focus a camera without rotating filters and special effects devices attached to the lens, and an improved filter adapter assembly which allows for easy placement and removal of additional filters and special effects devices placed on a camera lens.
2. Art Background
Special effects are often created in video and photographic productions using devices attached to the end of a lens of a camera, such as optical filters and matte boxes. For example, various types of color filters may be used to change or enhance a photographic or video image. For example, color correction filters adapt light sources to a particular color film being used. Neutral density filters reduce the light entering the lens and polarizing filters, depending upon the filter's orientation with the sun, reduces glare and light coming into a camera. An effect whereby stars or bursts of light from a light source are created by lines scratched on a glass or plastic filter is called a starburst or lined ruled filter.
Often times, many of these special effect filters and devices are used in conjunction with one another. For example, a polarized filter is used to reduce glare, while a color conversion filter functions to match lighting upon a subject with a particular type of color film used. In addition to the above two filters, a starburst filter may be used to produce stars or bursts of light. As can be seen from the above example, certain video and photographic works require a combination of filters used simultaneously. Furthermore, different combinations of devices are required for different shots and the camera-person or photographer may need to set-up quickly for the next shot.
Currently, there are two methods for mounting lenses and filters to a camera. The most common is a screw thread mount which is illustrated in FIG. 1(a) showing a screw thread mount filter. Screw thread mounts contain small threads on each end of a filter or lens which allow each device to be connected by screwing the devices together. Although this type of mounting renders filters and lenses physically secure to the rest of the camera, it does not provide easy removal and addition of devices. For example, dirt may enter into a thread grove resulting in less than optimal performance of the threads. Also, a co-efficient of expansion for an outer casing material of the lens and filter may cause the device to either contract or expand. Even if the screw thread mounts are not physically deformed or dirty, a user often finds the small threads are difficult to match and screw together properly. Also, cross threading can easily occur permanently damaging the threads and or the grooves. Therefore, the lenses and filters which are screw thread mounted are difficult to add and remove quickly. Because of this, bayonet mounting has been introduced. Unlike the screw thread mount, which will mate to any single lens reflex (SLR) camera regardless of the manufacturer, each manufacturer of the bayonet mount employs a slightly different system which results in incompatible filters and lenses. Therefore, it would be desirable to provide a system of mounting camera external devices which provide stability, easy addition and removal of external camera add-on devices.
An alternative to directly mounting filters with screw threads is to attach the filter to a camera lens with a filter adapter. FIG. 1(b) illustrates a filter adapter consisting of a step up/down ring, a Cokin universal filter holder, and a filter hood. The step up/down ring adapts particular threads of a camera lens to a chosen filter. The Cokin universal filter holder is adaptable to lenses which have a screw thread of 49 mm to 58 mm. The holder will house both square or round filters and more than one filter may be mounted at a time. A lens hood may be attached to the holder to shield the filter and lens from direct sunlight. This configuration is limited because if no filter is needed or a special effects device desired, the entire adapter assembly must be removed. Furthermore, various step up/down rings would be needed to accommodate different lenses used. It would be desirable for the camera-person or photographer to switch the filters quickly and easily. Therefore, it is an objective of this invention to provide a filter and special effects device add-on system where the add-on devices are securely mounted to a camera lens, compatible among different filters and lenses, and easy to remove and add.
In the current operation of a camera lens, when a focus adjustment is made, the entire barrel rotates including any additional filters or special effects devices attached. There are certain filters and special effects devices added on to a lens of a camera which must remain stationary, in a radial direction, to function properly. For example, polarization lenses must remain stationary to obtain the proper effect. An outdoor image taken with a polarized lens which is at a right angle with the sun will provide a darker blue sky and reduce glare than an image taken with a polarized filter not at a right angle with the sun. When superimposed graphical effects are desired, a camera may have a matte box attached to the end of the lens. The matte box blocks parts of a photographed or recorded image and thereby facilitates subsequent superimposing of graphics on the image. When using either polarizing filters or matte boxes in videotaping or photography, focusing presents a problem. It is a further objective of the present invention to provide a focusing lens while still allowing additional devices to remain stationary in a radial direction.
Images sought to be photographed are considered to be in focus when the image's reflection upon the cameras film is sharp and clear. A distance between a camera's lens and film is defined as focal length. In general, cameras are focused by changing the focal length. In whole lens focusing, an entire lens mechanism is shifted toward or away from the film. The actual distance in which the lens may move from the film is dependent upon the type of lens. Although less popular than whole lens focusing, front cell focusing only moves a rear element, the element furtherest from the camera body, toward or away from the lens while a front element is permanently focused upon infinity. Infinity, in this context, refers to a point at least 30 m from the camera.
As will be described in more detail below, a novel and simple solution to the above problems is provided by key alterations to the above described lens apparatus and filter mounting.